wp-admin unavailable after WP upgrade from 3.9.2 to 4.0 on FreeBSD 9.2

As soon as the new 4.0 version came out, I decided to upgrade my WordPress installation. Everything appeared to have went fine, but after the update I could not access the admin page any longer, I simply got a blank page. Scouring the forum on wordpress.org, I noticed a few others with the same issue, but no workable solution. My apache log only reported:192.168.0.11 – – [06/Sep/2014:23:05:18 +0200] “POST /wp-login.php HTTP/1.1” 500 – “http://www.ebbmar.com/wp-login.php” “Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.103 Safari/537.36”Ok, a 500 error (Internal server error). Could mean anything, really..

I managed to get error logging running on wordpress, by changing error_reporting(0) to error_reporting(1) at the bottom of the wp-config.php file. And when I tried to access the admin page, I was presented with a the error:Fatal error: Call to undefined function hash() in /usr/local/www/apache22/data/wp-includes/session.php on line 64

The row in question in session.php:return hash( ‘sha256’, $token );

For some reason it could not find the hash() function in PHP..
Found out that I had not installed php5-hash (don’t know why it worked in 3.9.2 or what has changed in the code), and simply installing the php5-hash port solved the issue.